Heat sink arrangement for electrical apparatus

ABSTRACT

A printed circuit board ( 120 ) includes an insulating substrate ( 120   a ) on which conductive films ( 120   b ) are formed. Semiconductor devices ( 8 ) disposed external to the printed circuit board ( 120 ) have their leads ( 24   a   , 24   b   , 24   c ) connected to the conductive films. A flexible portion ( 30 ) is formed in the insulating substrate ( 120   a ) at a location near the location where the leads ( 24   a   , 24   b   , 24   c ) are connected to the conductive films ( 120   b ).

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of copending U.S.patent application Ser. No. 11/439,412 filed May 22, 2006, now U.S. Pat.No. ______, the entirety of which is hereby incorporated by referenceherein.

FIELD OF THE INVENTION

This invention relates to dissipation of heat from an electricalapparatus, e.g. a power supply apparatus, employing semiconductordevices.

BACKGROUND OF THE INVENTION

Some electrical apparatus, e.g. a power supply apparatus, uses powersemiconductor devices as its components. Power semiconductor devices areconnected to a driver printed circuit board on which a driver circuitfor driving the power semiconductor devices is formed. The driverprinted circuit board is connected to a control printed circuit board onwhich a control circuit for controlling the driver circuit is formed.The power semiconductor devices are mechanically coupled to a heat sinkfor dissipating heat from the semiconductor devices. In order todownsize the power supply apparatus, the control printed circuit boardmay be mounted to the heat sink on which the power semiconductor devicesare mounted, with the driver printed circuit board mounted between thepower semiconductor devices and the control printed circuit board, tothereby assemble them into a single block. If, however, rigid boards areused for the control and driver printed circuit boards, dimensionalerrors and/or assemblage errors of such printed circuit boards may placestrain on the power semiconductor devices, causing the semiconductordevices to float up from the heat sink, which impedes normal heatdissipation and may break down the power semiconductor devices. Inaddition, the printed circuit boards themselves may be also strained.When such power supply apparatus is transported or removed to anotherplace, vibrations caused by the moving may be applied to the powersupply apparatus. Then, the vibrations are superposed on the strain onthe power semiconductor devices and the printed circuit boards, whichmay lead to breakdown of the printed circuit boards and the powersemiconductor devices.

JP 7-7167 U discloses use of a flexible board for connecting componentsmounted on a case to components mounted on a printed circuit boardattached to the case.

Similar flexible boards would be used to connect the above-describedpower semiconductor devices to the driver printed circuit board and toconnect the driver printed circuit board to the control printed circuitboard. This arrangement, however, would require two flexible boards inaddition to the driver and control printed circuit boards. In addition,a space for disposing the flexible boards must be secured, which impedesdownsizing of the power supply apparatus.

An object of the present invention is to provide an electricalapparatus, in which electrical components are prevented from beingbroken down and, still, which can be small in size.

SUMMARY OF THE INVENTION

An electrical apparatus according to an embodiment of the presentinvention includes a first printed circuit board formed of an insulatingsubstrate which is coated with an electrically conductive film. Thefirst printed circuit board may be a multi-layered board or asingle-layered board. An electrical component disposed external to thefirst printed circuit board has a rigid connector connected to theconductive film of the first printed circuit board. This connection ofthe connector to the conductive film may put strain to the connector,the electrical component and/or the first printed circuit board. Theinsulating substrate includes a flexible portion in the vicinity of theportion of the conductive film to which the electrical component isconnected.

The flexible portion may be formed by thinning a portion, which is tobecome the flexible portion, of the insulating substrate relative to theremaining portion.

The electrical component may be a semiconductor device mounted on a heatsink. In such case, the connector is a lead of the semiconductor device.The semiconductor device may be a power semiconductor device.

The first printed circuit board may be disposed near the heat sink. Inaddition, a second printed circuit board may be mounted to the surfaceof the heat sink opposite to the surface on which the semiconductordevice is mounted. The second printed circuit board is electrically andmechanically coupled to the first printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an electrical apparatus according to anembodiment of the present invention.

FIG. 2 is a front view of a heat dissipating portion of the electricalapparatus shown in FIG. 1.

FIG. 3 is a side view of the heat dissipating portion shown in FIG. 2.

FIG. 4 is a cross-sectional view along a line 4-4 in FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

An electrical apparatus according to an embodiment of the presentinvention is, for example, a power supply apparatus for use in weldingor electroplating. The power supply apparatus includes, as shown in FIG.1, an AC-to-DC converting circuit 4 for converting a three-phasecommercial AC voltage, for example, applied to power supply inputterminals 2 a, 2 b and 2 c, to a DC voltage. The AC-to-DC convertingcircuit 4 includes, for example, a rectifying circuit and a smoothingcircuit. The DC voltage from the AC-to-DC converting circuit 4 isapplied to a DC-to-AC converting circuit, e.g. an inverter 6, whichincludes plural, e.g. six, power semiconductor devices, e.g. IGBTs 8.The IGBTs 8 are connected in a full-bridge circuit configuration. The DCvoltage applied to the inverter 6 is converted therein to ahigh-frequency voltage, which is developed between two inverter outputterminals 10 a and 10 b. The high-frequency voltage isvoltage-transformed by a transformer (not shown), and thevoltage-transformed high-frequency voltage is converted to a DC voltageby a high-frequency-to-DC converting circuit (not shown). The resultingDC voltage is applied across a load, for example, between a torch andworkpiece in a welding machine, or between two electrodes forelectroplating.

Control signals for controlling the respective IGBTs 8 to convert the DCvoltage applied thereto to the high-frequency voltage are supplied tothe respective IGBTs 8 from a driver circuit 12. A control circuit 14gives instructions to the driver circuit 12 regarding the manner inwhich the IGBTs 8 should be controlled.

As shown in FIGS. 2 and 3, each of the IGBTs 8 is arranged in a chipform and mounted on a heat sink 16. Each IGBT 8 is the electricalcomponent as referred to in the accompanying Claims.

The heat sink 16 has an IGBT mounting surface 16 a of a rectangularshape, for example, as shown in FIG. 3, and also a number of fins 16 bon the opposite surface. The fins 16 b extend substantiallyperpendicularly to the mounting surface 16 a. Three IGBTs 8 are disposedin a row on the mounting surface 16 a, and their heat dissipatingsurfaces are in surface-contact with the mounting surface 16 a. Thethree IGBTs 8 are pressed against the mounting surface 16 a by means ofa retainer 18 a.

The retainer 18 a has three planar portions 181 a contacting a largerportion of the surfaces of the three IGBTs 8 opposite to the heatdissipating surfaces thereof. The three planar portions 181 a areconnected together by a connecting portion 181 b, which is bent, at aportion near a first side surface of the IGBTs 8, toward the mountingsurface 16 a of the heat sink 16. A lip portion 181 c integral with theconnecting portion 181 b is in contact with the mounting surface 16 a.The lip portions 181 c is fixed to the mounting surface 16 a by means oftwo screws 20 a. The respective IGBTs 8 are screwed to the mountingsurface 16 a by three screws 22 a extending, through the respectiveplanar portions 181 a of the retainer 18 and the IGBTs 8, into themounting surface 16 a. The remaining three IGBTs 8 are similarly mountedon the mounting surface 16 a of the heat sink 16 by means of a retainer18 b and screws 20 b and 22 b, which are similar to the retainer 18 aand the screws 20 a and 22 a.

Each IGBT 8 has three leads 24 a, 24 b and 24 c. The three leads 24 a-24c of each IGBT 8 extend from a second side surface thereof, which isopposite to the first side surface, in the direction away from theretainers 18 a and 18 b, and are bent in a direction away from the heatsink 16. The leads 24 a-24 c are made of a material having highrigidity, e.g. metal. The leads 24 a-24 c are the connector referred toin the accompanying Claims. The leads 24 a-24 c are electrically andmechanically connected by, for example, soldering, to patternedconductors formed at predetermined locations on a printed circuit board120, on which the driver circuit 12 is arranged. This eliminates theneed for use of wires for electrical connections between the respectiveIGBTs 8 and the printed circuit board 120. The printed circuit board 120is disposed, being spaced from and substantially in parallel with themounting surface 16 a of the heat sink 16. The printed circuit board 120slightly overlaps the mounting surface 16 a, and the remaining portionlies outside the mounting surface 16 a. The printed circuit board 120 isthe first printed circuit board referred to in the accompanying Claims.

The printed circuit board 120 has its portion remote from the mountingsurface 16 a secured to a printed circuit board 140, on which thecontrol circuit 14 is arranged, by means of three screws 32. The drivercircuit on the printed circuit board 120 is electrically connected tothe control circuit 14 on the printed circuit board 140. The printedcircuit board 140 is disposed, being spaced from and in parallel withthe outermost fin 16 b, and is secured to the outermost fin 16 b bymeans of a plurality of spacers 26 and screws 28. Thus, the majorsurfaces of the printed circuit board 140 lie perpendicular to the IGBTs8. In this manner, the heat sink 16 with the IGBTs 8 mounted thereon andthe printed circuit boards 120 and 140 form one block. The printedcircuit board 140 is the second printed circuit board referred to in theaccompanying Claims.

Generally, the printed circuit boards 120 and 140 are formed of a rigidor hard insulating materials, e.g. a glass epoxy material, with aelectrically conductive film, e.g. copper foil. Electric components aresoldered to the conductive films at predetermined locations. If,therefore, the dimensional precision of the printed circuit boards 120and 140 is low, and/or the precision of assemblage of the IGBTs 8 andprinted circuits boards 120 and 140 is low, strain may be put on theIGBTs 8, which causes the IGBTs 8 to rise up from the mounting surface16 a, resulting in insufficient heat dissipation from the IGBTs 8. Insome cases, strain is put on the leads 24 a-24 c of the IGBTs 8, causingthe rigid leads 24 a-24 c to snap or bend.

In order to solve this problem, according to this embodiment, a flexibleportion 30 is formed in the printed circuit board 120. As shown in FIG.4, the printed circuit board 120 is a multi-layered printed circuitboard formed of an epoxy glass material 120 a within which a conductivepattern formed of plural, e.g. three, conductive films 120 b, isarranged. The flexible portion 30 is formed by removing part of theepoxy glass material 120 a from the opposite major surfaces of the epoxyglass material 120 a, at a location slightly spaced in the directionaway from the leads 24 a-24 c. The flexible portion 30 extends in thedirection along which the leads 24 a-24 c are arranged.

The flexible portion 30 can absorb strain which may be generated, asdescribed above, when the dimensional precision of the printed circuitboards 120 and 140 and/or the precision of assembling the IGBTs 8 andthe printed circuit boards 120 and 140 are low. Then, it never happensthat the contact of the IGBTs 8 with the heat sink 16 becomes defective,or that the leads 24 a-24 c snap or bend. Since the flexible portion 30is formed by removing part of the insulating material of the printedcircuit board 120, there is no need for preparing a separate, flexibleprinted circuit board for connection of the IGBTs 8 and the printedcircuit board 120, in order for strain to be absorbed.

The present invention has been described as being embodied in a powersupply apparatus for welders or electroplating machines. However, thepresent invention is not limited to them, but it can be embodied in anyelectrical apparatuses in which electrical components need be connectedto printed circuit boards. Further, the flexible portion has beendescribed as being formed in a multi-layered printed circuit board, but,when the printed circuit board used includes a conductive film only onone surface, the flexible portion can be formed by removing part of theinsulating material from the other surface of the printed circuit board.In the described embodiment, the leads of the semiconductor devices aresoldered to the printed circuit board 120, but they may be electricallyand mechanically connected by screwing, caulking or the like.Furthermore, other semiconductor devices, such as bipolar transistorsand FETs, than IGBTs may be used.

1. An electrical apparatus comprising: a multi-layered printed circuitboard formed of a glass epoxy material, said multi-layered printedcircuit board having opposing two major surfaces and comprising oneelectrically conductive pattern formed within said glass epoxy material,said conductive pattern being formed by a plurality of electricallyconductive films; and a plurality of electrical components disposed in aline external to said multi-layered printed circuit board, saidelectrical components respectively having rigid connectors connected torespective ones of said plurality of electrical conductive films;wherein a flexible portion is formed in said multi-layered printedcircuit board at a location near a location where said connector of eachof said electrical components is connected to an associated one of saidconductive films, and said flexible portions are formed by removing saidepoxy glass material from both of said opposing major surfaces, saidflexible portions being formed in a line extending along said line inwhich said electrical components are disposed.
 2. The electricalapparatus according to claim 1, wherein said electrical components aresemiconductor devices mounted on a heat sink; said connectors are leadsof said semiconductor devices and extend through said opposing two majorsurfaces of said multi-layered printed circuit board; and saidmulti-layered printed circuit board is disposed near said heat sink. 3.The electrical apparatus according to claim 2, wherein a second printedcircuit board is mounted on a surface of said heat sink different fromthe surface on which said semiconductor devices are mounted, said secondprinted circuit board being disposed perpendicular to one of said majorsurfaces of said multi-layered printed circuit board; and said secondprinted circuit board is connected electrically and mechanically to saidmulti-layered printed circuit board.